The invention relates to pump assemblies, throttling valves and pumping methods where the output of the pump assembly is controlled by throttling inlet flow to the pump. The pump assembly, valve and method may be used to pressurize engine oil used in a Hydraulic Electronic Unit Injector (HEUI) diesel engine fuel system.
Diesel engines using HEUI fuel injectors are well known. A HEUI injector includes an actuation solenoid which, in response to a signal from the diesel engine electronic control module, opens a valve for an interval to permit high pressure engine oil supplied to the injector to extend a fuel plunger and inject fuel into the combustion chamber.
HEUI injectors are actuated by oil drawn from the sump of the diesel engine by the diesel engine oil pump and flowed to a high pressure pump assembly driven by the diesel engine. The pump assembly pumps engine oil at high pressure into an oil manifold or compression chamber. The manifold or chamber is connected to the HEUI injectors. Except for large engines, the high pressure pump assembly typically includes a swash plate pump using axial pistons and having an output dependent upon the speed of the diesel engine. Large engines sometimes use a variable angle swash plate pump where the output can be varied independently of engine speed.
The pump assembly pumps oil at a rate depending on engine speed. The output must be sufficient to meet maximum flow requirements. The pressure of the oil in the oil manifold or chamber is controlled by an injection pressure regulator (IPR) valve in response to signals received from the electronic control module for the engine. The IPR valve limits the pressure in the pumped oil by flowing excess high pressure oil back into the engine sump.
Most HEUI injection systems use fixed output oil pump assemblies which pump oil at a rate dependent upon the rotational speed of the diesel engine and independent of the actual instantaneous flow requirements for the engine. The pump operates at full capacity at all times, even when excess high pressure oil must be flowed or relieved back to the sump immediately to limit the pressure of the oil in the manifold as required by the engine electronic control module. Considerable power is required to drive the pump assembly at full capacity all the time. The energy required to pump high pressure oil which is relieved back to the sump is wasted and decreases the fuel economy of the diesel engine. Energy is converted to heat when high pressure oil is exhausted without doing useful work. The heat in the returned oil must be dissipated, typically by a heat exchanger. Heat exchanger capacity must be increased to accommodate the additional heat load.
Therefore, there is a need for an improved high pressure pump assembly and method for use in a HEUI diesel engine. The pump assembly should pump engine oil into a high pressure oil manifold or chamber in a variable amount sufficient to maintain the desired instantaneous pressure in the manifold without substantial overpumping. Return of pressurized high pressure oil to the sump should be minimized. The pump in the assembly should be capable of pumping a variable output and should be less expensive and less complicated than present HEUI pumps.
The invention is an improved pump assembly, inlet throttle valve, high pressure pump and method where the output of the pump assembly is varied by controlling or throttling the input flow to the assembly.
The pump assembly is particularly useful in pressurizing oil used to actuate HEUI fuel injectors for diesel engines. The improved pump assembly includes an inlet throttle valve which controls inlet flow of oil from the diesel engine oil pump to the high pressure pump. The inlet throttle valve throttles or restricts the volume of oil flowing into the high pressure pump in response to signals received from the engine electronic control module.
The high pressure pump includes a crank which reciprocates pistons in bores. Oil supplied to the high pressure pump through the inlet throttle valve flows into a crank chamber and into the bores during return strokes, is pressurized during pumping strokes and is pumped past poppet outlet valves to a high pressure manifold. When the inlet throttle valve is fully opened sufficient oil flows into the crank chamber to fill the pumping chambers during the return strokes and oil is pumped into the manifold at full pump capacity. When the inlet throttle valve is partially closed a reduced amount of oil flows into the crank chamber, partially fills the bores and is pumped at less than full pump capacity.
The inlet throttle valve is controlled by an injection pressure regulator valve having a main stage valve for flowing pressurized oil from the pump outlet into the sump when necessary to limit manifold pressure, and an electrically modulated pilot stage valve.
The pilot stage valve includes a solenoid modulated by a signal from the electronic control module to restrict pilot flow of oil from the pump outlet. To reach the pilot stage, oil from the pump outlet must pass through a restrictive orifice within a main stage spool, thereby regulating the spool against the closing force of a spring. From the pilot stage, pilot flow passes through a downstream restrictive orifice and then returns to the engine sump along with any drain flow from the main stage of the injection pressure regulating valve. The pressure of the oil in the chamber between the pilot stage and the downstream restrictive orifice is determined by pilot flow rate. The chamber between the pilot stage and the downstream restrictive orifice communicates with the end of the inlet throttle spool and acts on the spool area to generate a force that shifts the inlet throttle valve spool in a closing direction against a spring and inlet pressure acting on the spool area to control or throttle flow of oil into the crank chamber.
Control or throttling of the flow of oil into the crank chamber controls the flow rate of high pressure oil pumped from the outlet into the high pressure manifold by the pump as necessary to maintain the desired pressure in the manifold. The pump assembly flows a volume of oil sufficient to maintain the desired pressure in the manifold. The pump assembly meets flow requirements while only rarely pumping at full capacity. Less power is required to pump HEUI oil. Reduction in the power required to drive the high pressure pump increases the fuel efficiency of the diesel engine. The necessity to cool sump oil is reduced.
The pump assembly includes two 90xc2x0 banks with two single high pressure check valve piston pumps in each bank. Each pump includes a piston in a bore and a spring in the bore biasing the piston against a slipper socket and holding the slipper against a crank eccentric. The eccentrics are oriented 180xc2x0 out of phase so that the pistons in the four pumps are moved through pumping strokes spaced 90xc2x0 apart to provide evenly spaced high pressure oil pumping cycles during each 360xc2x0 rotation of the crank. Pulses may be timed to occur during injection events.
Each high pressure piston pump includes a bore extending toward the axis of a crank shaft, a piston in the bore and a check valve assembly mounted in the outer end of the bore and connected to a high pressure passage. The check valve assemblies are mounted in the bores by pressing sleeves into the outer cylindrical ends of the bores and then pressing plugs into the sleeves to form high pressure joints between the plugs, sleeves and bores. The check valve assemblies are mounted without cutting threads in the bores and without the complexity of machining and contamination that are characteristic of threaded plugs. The check valve seat is retained in the sleeve by a tapered engagement that forces the sleeve radially outward to improve sealing and increase sleeve retention force.
Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention.